Application transparent autonomic availability on a storage area network aware file system

ABSTRACT

Techniques are provided for locating data. Mapping information for blocks associated with a file is provided. It is determined that a copy service has copied source blocks to target blocks. It is determined whether the mapping information should be updated to refer to the target blocks. Then, updated mapping information is provided in response to determining that the mapping information should be updated to refer to the target blocks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S. Pat. No. 7,383,406, “APPLICATION TRANSPARENT AUTONOMIC AVAILABILITY ON A STORAGE AREA NETWORK AWARE FILE SYSTEM”, having application Ser. No. 10/994,149, filed Nov. 19, 2004, the entire contents of which is incorporated herein by reference.

BACKGROUND

1. Field

Implementations of the invention relate to application transparent autonomic availability on a Storage Area Network (SAN) aware file system.

2. Description of the Related Art

Computing systems often include one or more host computers (“hosts”) for processing data and running application programs, direct access storage devices (DASDs) for storing data, and a storage controller for controlling the transfer of data between the hosts and the DASD. Storage controllers, also referred to as control units or storage directors, manage access to a storage space comprised of numerous hard disk drives, otherwise referred to as a Direct Access Storage Device (DASD). Hosts may communicate Input/Output (I/O) requests to the storage space through the storage controller.

Storage controllers may provide copy services. With the copy services, data on one storage device, such as a DASD, may be copied to the same or another storage device so that access to data volumes can be provided from two different devices or to have a backup copy.

International Business Machines Corporation (IBM), the assignee of the subject patent application, provides remote copy services for maintaining remote copies of data at a secondary storage device, including extended remote copy (XRC) and peer-to-peer remote copy (PPRC). These systems provide techniques for recovering data updates between a last, safe backup and a system failure. Such data shadowing systems can also provide an additional remote copy for non-recovery purposes, such as local access at a remote site.

Another example of a copy service is a point-in-time copy, which involves physically copying all the data from source volumes to target volumes so that the target volume has a copy of the data as of a point-in-time. A point-in-time copy can also be made by logically making a copy of the data and then only copying data over when necessary, in effect deferring the physical copying, and this is referred to as an “instant virtual copy” operation or “fast replicate function.”

Instant virtual copy operations work by modifying metadata such as relationship tables or pointers to treat a source data object as both the original and copy. In response to a host's copy request, the storage subsystem immediately reports creation of the copy without having made any physical copy of the data. Only a “virtual” copy has been created, and the absence of an additional physical copy is completely unknown to the host. The host or storage subsystem may even proceed to create an actual, physical copy of the original data object during background processing, or at another time.

One such instant virtual copy operation is known as a FlashCopy® operation. Further details of the FlashCopy® operations are described in the commonly assigned U.S. Pat. No. 6,661,901, issued on Aug. 26, 2003, entitled “Method, System, and Program for Maintaining Electronic Data as of a Point-in-Time”, which patent application is incorporated herein by reference in its entirety.

Typically, backup of a file via a copy services operation provided by a storage controller is non-disruptive to a host computer. However, the process of recovering a file (i.e., copying the file from a backup copy to the original (“source”) copy) may be disruptive. The host computer needs to know of and maintain the location of where the data is being copied. This becomes especially difficult when using block based copy services, which copy portions of a volume rather than an entire volume of data. If the host computer knows where all of the backup copies are, recovery of a file or Logical Unit Number (LUN) is still a manually intensive procedure. A LUN may be described as a unique number that may identify a specific disk and is typically used to refer to a disk having that LUN.

Also, currently, when a storage controller fails, a file system at a host computer uses copy services to migrate data. However, this is not an efficient process.

Therefore, there is a continued need in the art for improved file access and migration.

SUMMARY OF THE INVENTION

Provided are an article of manufacture, system, and method for locating data. Mapping information for blocks associated with a file is provided. It is determined that a copy service has copied source blocks to target blocks. It is determined whether the mapping information should be updated to refer to the target blocks. Then, updated mapping information is provided in response to determining that the mapping information should be updated to refer to the target blocks.

Techniques are also provided for accessing a copy of data when a source of the data is inaccessible. It is determined that source blocks are unavailable. Target blocks that are a copy of the unavailable source blocks are located using data in a metadata store. Indicators pointing to the source blocks are switched to point to the target blocks. Mapping information is updated at one or more client computers to access the target blocks instead of the source blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers represent corresponding parts throughout:

FIG. 1 illustrates a computing environment in which certain implementations of the invention are implemented.

FIG. 2 illustrates client computers in accordance with certain implementations of the invention.

FIG. 3 illustrates metadata servers in accordance with certain implementations of the invention.

FIG. 4 illustrates a metadata store in accordance with certain implementations of the invention.

FIG. 5 illustrates a storage system in accordance with certain implementations of the invention.

FIG. 6 illustrates logic for processing opening a file in accordance with certain implementations of the invention.

FIG. 7 illustrates logic for updating mapping information in accordance with certain implementations of the invention.

FIG. 8 illustrates logic for error processing in accordance with certain implementations of the invention.

FIG. 9 illustrates logic for processing read and write requests that are in-process when a storage controller fails in accordance with certain implementations of the invention.

FIG. 10 illustrates an architecture of a computer system that may be used in accordance with certain implementations of the invention.

DETAILED DESCRIPTION OF THE IMPLEMENTATIONS

In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrate several implementations of the invention. It is understood that other implementations may be utilized and structural and operational changes may be made without departing from the scope of implementations of the invention.

FIG. 1 illustrates, in a block diagram, a computing environment in accordance with certain implementations of the invention. One or more client computers 100 a . . . 100 n are connected via a network 170 to a metadata server cluster 130 and via a storage network 180 to a storage system 150. The storage network 180 provides direct data transfer between client computers 100 a . . . 100 n and storage system 150.

Each client computer 100 a . . . 100 n includes a file system 120 a . . . 120 n with a cache 122 a . . . 122 n, respectively. The client computers 100 a . . . 100 n may run any operating system 108 a . . . 108 n (FIG. 2), such as an AIX® operating system, a Linux® operating system, a Windows® 2000 operating system, a Windows® XP operating system, a Solaris® operating system, a UNIX operating system or HP-UX operating system. The client computers 100 a . . . 100 n may also be referred to as “storage clients”.

The file system 120 a . . . 120 n may be called an installable file system (IFS) on client computers running certain operating systems (e.g., a Windows® 2000 operating system, a Windows® XP operating system, or HP-UX operating system) and may be called a virtual file system (VFS) on client computers running certain other operating systems (e.g., AIX® operating system, Linux® operating system or a Solaris® operating system). The file systems 120 a . . . 120 n at the client computers 100 a . . . 100 n may be referred to as storage controller client file systems.

The file systems 120 a . . . 120 n direct metadata operations to the metadata server cluster 130 and direct data operations to storage system 150 attached to a high-speed storage network 180. The file systems 120 a . . . 120 n make the metadata that is visible to each client computer 100 a . . . 100 n operating system, as well as any application programs that a client computer 100 a . . . 100 n runs, look identical to metadata read from a native, locally-attached file system. The file systems 120 a . . . 120 n support locking and caching of data.

Each client computer 100 a . . . 100 n may comprise any computing device known in the art, such as a server, mainframe, workstation, personal computer, hand held computer, laptop telephony device, network appliance, etc.

The metadata server cluster 130 includes metadata servers 132 a . . . 132 m. An admin client computer 190 may be optionally connected to metadata server cluster 130 to allow an administrator to submit commands directly to one or more metadata servers 132 a . . . 132 m. Each metadata server 132 a . . . 132 m implements a SAN file system catalog that stores mappings between files and source blocks on storage devices making up the file. The mappings are stored in the metadata store 140.

A metadata store is connected to the storage network 180. The metadata servers 132 a . . . 132 m maintain data in the metadata store 140 including, for example, locations of data in storage system 150 and how frequently data is accessed by each client computer 100 a . . . 100 n.

The storage system 150 includes one or more storage controllers 152 a . . . 152 q and includes shared storage pools 154 for storing data (e.g., files). Although one storage system 150 is illustrated, multiple storage systems may be connected to the storage network 180.

A SAN may be described as a high-speed sub-network of shared storage devices. A storage device may be described as any component that is capable of storing data. Multiple metadata servers 132 a . . . 132 m have access to storage devices in the storage system 150. A SAN aware file system may be described as including the metadata server cluster 130, the metadata store 140, the storage system 150, the storage network 180, and the virtual and installable file systems 120 a . . . 120 n. Thus, a unified file system in a clustered environment is illustrated in FIG. 1.

The networks 170 and 180 may each comprise any type of network, such as, for example, a Storage Area Network (SAN), a Local Area Network (LAN), Wide Area Network (WAN), the Internet, an Intranet, etc.

FIG. 2 illustrates client computers 100 a . . . 100 n in accordance with certain implementations of the invention. Each client computer 100 a . . . 100 n includes one or more Central Processing Units (CPU) 102 a . . . 102 n and a system memory 104 a . . . 104 n, which may be implemented in volatile and/or non-volatile devices. One or more client applications 106 a . . . 106 n, an operating system 108 a . . . 108 n, and one or more error recovery systems 112 a . . . 112 n may be stored in the system memory 104 a. The operating system 108 a . . . 108 n may include one or more device drivers 110 a . . . 110 n. The error recovery systems 112 a . . . 112 n and device drivers 110 a . . . 110 n may be used when switching indicators from one set of blocks to another (e.g., from source blocks to target blocks) in order to ensure a data consistent switch. Since I/O may be occurring in a continuous stream, the metadata server 132 a . . . 132 m and/or copy service 158 a . . . 158 q (FIG. 5) may instruct the storage controller 152 a . . . 152 q to return an error indication at the moment the blocks are switched to the new blocks to use. This will cause the error recovery system 112 a . . . 112 n and/or the device driver 110 a . . . 110 n to perform a retry operation, and as part of the retry operation, the mapping of local (virtual) block addresses to physical storage is updated. The next I/O then proceeds to the new location of the data.

In normal I/O systems, when a permanent error is detected, the device driver 110 a . . . 110 n and/or error recovery system 112 a . . . 112 n returns an error indication to the requesting program. This normally results in an abnormal termination of the application program, which would result in an application outage. In implementations of the invention, the error recovery system 112 a . . . 112 n performs additional processing. In particular, initially, an error is returned from a device performing an I/O operation. The error recovery system 112 a . . . 112 n determines whether the device is a virtual device being managed by a SAN aware file system. If the virtual device is not being managed by SAN aware file system, the error is returned to the I/O request for action. If the virtual device is being managed by a SAN aware file system, the error recovery system 112 a . . . 112 n notifies the metadata server 132 a . . . 132 m or notifies the client computer 100 a . . . 100 n, which then notifies the metadata server 132 a . . . 132 m, that an error has occurred. The error recovery system 112 a . . . 112 n waits for a policy decision to be made on redirecting I/O. The metadata server 132 a . . . 132 m (or other policy engine) decides whether to switch indicators to data, which data to switch to, and performs the switch operation. The client computer 100 a . . . 100 n is updated with the new mapping, and notifies the error recovery system 112 a . . . 112 n that its wait is over. If the data was remapped, the error recovery system 112 a . . . 112 n retries an operation using the new address. If the data was not remapped, the error recovery system 112 a . . . 112 n returns an error. In alternative implementations, the client computer 100 a . . . 100 n may be aware of whether the new copy of the data is writeable or not, and the error recovery system 112 a . . . 112 n may report an error if the request is for a write and the data was mapped to a read-only location.

FIG. 3 illustrates metadata servers 132 a . . . 132 m in accordance with certain implementations of the invention. Each metadata server 132 a . . . 132 m includes system memory 134 a . . . 134 m, which may be implemented in volatile and/or non-volatile devices. Each system memory 134 a . . . 134 m includes a data manager 136 a . . . 136 m and one or more server applications 138 a . . . 138 m.

Each metadata server 132 a . . . 132 m is able to keep track of multiple references to data source blocks and copies of the data source blocks. For ease of reference, the copies of the data source blocks will be referred to as “target blocks.” A set of related source blocks may be described as a data unit (e.g., a file). Each metadata server 132 a . . . 132 m also tracks the location of each client computer 100 a . . . 100 n.

Each metadata server 132 a . . . 132 m acts as a catalogue for the SAN aware file system by storing mappings between files and source and target blocks making up the file. Each metadata server 132 a . . . 132 m also works with copy services 158 a . . . 158 q (FIG. 5) provided, for example, by the storage system 150. The copy services allow for policy based copy services, such as point-in-time copy services, continues copy services, etc. Each metadata server 132 a . . . 132 m may work with other application programs or SAN elements to execute the copy services. That is, the copy services may be provided in various forms, such as in the form of an application executing on a server computer or in a SAN fabric element.

As data is copied via the copy services, each metadata server 132 a . . . 132 m tracks the relationship between the source blocks and copies of those blocks, regardless of the type of copy service (e.g., point-in-time copy service or continuous copy service). Moreover, each metadata server 132 a . . . 132 m is able to swap the reference for a file's blocks from the source blocks to a copy of the source blocks (i.e., “target blocks”), which makes the target blocks the new source blocks.

FIG. 4 illustrates a metadata store 140 in accordance with certain implementations of the invention. Metadata store 140 includes mapping information 142. The mapping information includes a table with rows associated with a file. For each file, the mapping information includes a filename, source blocks that indicate locations of source blocks for the file, 1-X target blocks, and a session identifier. The 1-X target blocks represent one or more copies of source blocks and provide locations of copies of the source blocks. A session is a set of copy service relationships that represent a set of data being maintained in a consistent state. Each target copy of a file (made up of target blocks) may share a session or have its own session. Additionally, the metadata store 140 may store information that describes the locations of data units, how frequently each data unit is accessed by each client computer 100 a . . . 100 n, etc.

FIG. 5 illustrates a storage system 150 in accordance with certain implementations of the invention. The storage system 150 provides one or more storage controllers 152 a . . . 152 q and shared storage pools 154. Each storage controller 152 a . . . 152 q provides copy services 158 a . . . 158 q. Each shared storage pool 156 a . . . 156 p provides shared storage devices. In certain implementations, storage devices (e.g., LUNs) are grouped into storage pools to allow policy-based management based on service class attributes such as performance and reliability. In certain implementations, each storage controller 152 a . . . 152 q is connected to a storage pool or one or more storage devices (e.g., LUNs) within a storage pool. The storage pools 156 a . . . 156 p may each include, for example, an array of storage devices, such as Direct Access Storage Devices (DASDs), Just a Bunch of Disks (JBOD), Redundant Array of Independent Disks (RAID), a virtualization device, etc.

FIG. 6 illustrates logic for processing opening a file in accordance with certain implementations of the invention. Control begins at block 600 with an application program 106 a . . . 106 n at a client computer 100 a . . . 100 n sending a request for a file to the metadata server 132 a . . . 132 m when opening the file. In block 602, the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m determines which blocks for the file should be made available to the client computer 100 a . . . 100 n based on one or more factors. For example, the blocks for the file may be source blocks or target blocks. The blocks may be selected based on their location to the client computer 100 a . . . 100 n, based on connections that the client computer 100 a . . . 100 n has with the storage system 150, based on which blocks are being least referenced by other client computers 100 a . . . 100 n, based on a read/write access pattern, based on reliability requirements, etc.

In block 604, the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m sends mapping information to the client computer 100 a . . . 100 n. In certain implementations, the mapping information provides indirect pointers to the blocks. In block 606, the application program 106 a . . . 106 n at the client computer 100 a . . . 100 n uses the mapping information to determine the location of the blocks of the file and to access the blocks.

FIG. 7 illustrates logic for updating mapping information in accordance with certain implementations of the invention. Control begins at block 700 with a copy service 158 a . . . 158 q copying source blocks of data to target blocks of data. In block 702, the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m updates the metadata store 140 with the locations of the target blocks for the source blocks. In block 704, the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m determines which (if any) client computers 100 a . . . 100 n should be sent updated mapping information for the newly copied target blocks. For example, if client computer 100 a received mapping information for a first set of target blocks associated with FILEA, but the newly created target blocks, which are also associated with FILEA, are determined to be a “more available” set of blocks for client computer 100 a, then the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m sends updated mapping information to the client computer 100 a for the newly copied target blocks. A set of blocks that are “more available” blocks may be described as a set of blocks that are not accessed as often as another set of blocks.

In block 706, the data manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m updates caches of the appropriate client computers 100 a . . . 100 n with updated mapping information. In block 708, an application program 106 a . . . 106 n at the client computer 100 a . . . 100 n uses the updated mapping information to access the blocks for a file the next time access is desired. Thus, with the processing described in FIG. 6 and FIG. 7, a client computer 100 a . . . 100 n accesses the metadata server 132 a . . . 132 m once on opening a file to obtain mapping information for blocks for that file. Then, the metadata server 132 a . . . 132 m automatically updates mapping information based on determining whether a newly created target copy may be a better match for the client computer 100 a . . . 100 n.

During normal file system operations, if a continuous copy of data is appropriate for a file, a request to create a continuous copy of blocks for a file may be made. The request may be made, for example, by the metadata server 132 a . . . 132 m based on a copy policy at the file system level, by using the admin client computer 190 to insert a user-specified request, or by an application program 106 a. The metadata server 132 a . . . 132 m would record in the metadata store 140 the location of the target blocks for that file. Once the copy is made of the blocks of the file, updates may be made to the target blocks as updates are made to the source blocks. Then, the SAN aware file system may switch between the source blocks and target blocks with no impact to any application programs.

FIG. 8 illustrates logic for error processing in accordance with certain implementations of the invention. During normal system operations, an error may occur in the SAN aware file system such that source blocks for a file are no longer accessible. Implementations of the invention autonomically address this problem. In FIG. 8, control begins at block 800 with a determination that a storage controller 152 a . . . 152 q has failed. In certain implementations, an application program 106 a . . . 106 n and/or client computer 100 a . . . 100 n determine that a storage controller 152 a . . . 152 q has failed when a request submitted to a storage controller 152 a . . . 152 q is not processed (e.g., within a certain period of time). In certain implementations, optionally, the application program 106 a . . . 106 n and/or client computer 100 a . . . 100 n resubmits the request to the storage controller 152 a . . . 152 q.

In block 802, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m is notified of the failure of the storage controller 152 a . . . 152 q. For example, the notification may come from the application program 106 a . . . 106 n and/or client computer 100 a . . . 100 n. When a storage controller 152 a . . . 152 q fails, source blocks that were accessed through that storage controller 152 a . . . 152 q may no longer be accessible. In block 804, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m determines, using one or more policies, whether it is appropriate to switch indicators pointing to the inaccessible source blocks to target blocks that are accessible. These policies are used to determine when it is appropriate to switch indicators from original source blocks to target blocks, making the target blocks the new source blocks. One example of such a policy is: “If all the data contained in the session to which this data belongs is consistent, then switch the block indicators and recover the data transparently; if the data is not consistent, then do not switch the indicators and allow normal error processing to occur.”

In block 806, if it is determined to be appropriate to switch indicators, processing continues to block 808, otherwise, processing is done. In block 808, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m locates target blocks for each set of inaccessible source blocks using the metadata store 140. When more than one set of target blocks are available for one set of inaccessible source blocks, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m selects one set of target blocks based on one or more policies. One example of such a policy is: “If the original source blocks were being copied using a continuous copy service, switch to a set of target blocks which is also capable of being copied continuously.” Another example of such a policy is: “Switch to the target blocks that are physically closest to the application server that will be processing the recovered data.” Yet another example of such a policy is: “Switch to the highest reliability copy of the data”.

In block 810, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m recognizes that the copy relationship is suspended between the inaccessible source blocks and the located target blocks. In block 812, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m switches indicators from the inaccessible source blocks to point to the located target blocks, making the target blocks the “new source blocks.” In block 814, the data location manager 136 a . . . 136 m at the metadata server 132 a . . . 132 m updates the metadata store 140. For example, for each file whose blocks are on the failed storage controller 152 a . . . 152 q storage (e.g., LUNs), mapping information 142 is updated so that the indicators to the original source blocks for these files are set to point to the new source blocks. Also, the new source blocks are no longer treated as target blocks in the mapping information 142.

In block 816, the data location manager 136 a . . . 136 m at metadata server 132 a . . . 132 m updates the appropriate client computer caches with updated mapping information. For example, if client computer 100 a had mapping information for the source blocks that became inaccessible, the metadata server 132 a . . . 132 m would update the cache for client computer 100 a to access the located target blocks (also referred as “new source blocks”) instead.

In block 818, the application program 106 a . . . 106 n at the client computer 100 a . . . 100 n whose cache has been updated would use the updated mapping information on its next access of the blocks. Additionally, in block 820, the data location manager 136 a . . . 136 m uses copy services 158 a . . . 158 q to make a copy of the located target blocks (“new source blocks”). In certain implementations, if there were more than one set of target blocks for a set of inaccessible source blocks, then a copy of the located target blocks may not be made.

FIG. 9 illustrates logic for processing read and write requests that are in-process when a storage controller 152 a . . . 152 q fails in accordance with certain implementations of the invention. Control begins at block 900 with the data manager 136 a . . . 136 q at the metadata server 132 a . . . 132 q redirecting in-process read requests to the new source blocks after the indicators have been switched (block 812 of FIG. 8). In block 902, the data manager 136 a . . . 136 q at the metadata server 132 a . . . 132 m freezes writes to the storage controller 152 a . . . 152 q. In block 904, the data manager 136 a . . . 136 q at the metadata server 132 a . . . 132 m redirects the write requests to the new source blocks (i.e., the target blocks located in block 808 of FIG. 8).

Thus, when a client computer 100 a . . . 100 n requests a file, the data manager 136 a . . . 136 q at the metadata server 132 a . . . 132 m sends mapping information to the client computer 100 a . . . 100 n for a preferred set of blocks (e.g., source blocks or target blocks). In this manner, the data manager 136 a . . . 136 q at the metadata server 132 a . . . 132 m is able to provide blocks having the highest availability based on various factors.

Additionally, certain implementations make use of SAN aware file systems and their ability to track locations of source blocks and target blocks for a file using a cataloging facility (e.g., metadata server). In particular, the SAN aware file system is able to track a source block for a file along with copies of that source block. Additionally, the SAN aware file system is able to replace a file with a prior copy or a synchronous copy by changing references from the source blocks to a set of target (“copy”) blocks and by making the target blocks the new source blocks. This change is transparent to application programs on the client computers 100 a . . . 100 n.

Moreover, implementations use copy services capabilities provided in the SAN aware file system to migrate data quickly and efficiently. In certain implementations, underlying SAN hardware and copy services software of a SAN aware file system are used to migrate data from one storage controller to another storage controller for fast data migration.

IBM and AIX are registered trademarks or common law marks of International Business Machines Corporation in the United States and/or other countries. Windows is a registered trademark of Microsoft Corporation in the United States and/or other countries. Solaris is a registered trademark or common law mark of Sun Microsystems in the United States and/or other countries. Linux is a registered trademark of Linus Torvalds in the United States and/or other countries. HP-UX is an Open Group UNIX 95 branded product in the United States and/or other countries. UNIX is a registered trademark or common law mark of The Open Group in the United States and/or other countries.

Additional Implementation Details

The described implementations may be implemented as a method, apparatus or article of manufacture using programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. The terms “article of manufacture” and “circuitry” as used herein refer to a state machine, code or logic implemented in hardware logic (e.g., an integrated circuit chip, Programmable Gate Array (PGA), Application Specific Integrated Circuit (ASIC), etc.) or a computer readable medium, such as magnetic storage medium (e.g., hard disk drives, floppy disks, tape, etc.), optical storage (CD-ROMs, optical disks, etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic, etc.). Code in the computer readable medium is accessed and executed by a processor. When the code or logic is executed by a processor, the circuitry may include the medium including the code or logic as well as the processor that executes the code loaded from the medium. The code in which implementations are implemented may further be accessible through a transmission media or from a server over a network. In such cases, the article of manufacture in which the code is implemented may comprise a transmission media, such as a network transmission line, wireless transmission media, signals propagating through space, radio waves, infrared signals, etc. Thus, the “article of manufacture” may comprise the medium in which the code is embodied. Additionally, the “article of manufacture” may comprise a combination of hardware and software components in which the code is embodied, processed, and executed. Of course, those skilled in the art will recognize that many modifications may be made to this configuration, and that the article of manufacture may comprise any information bearing medium known in the art.

The logic of FIGS. 6-9 describes specific operations occurring in a particular order. In alternative implementations, certain of the logic operations may be performed in a different order, modified or removed. Moreover, operations may be added to the above described logic and still conform to the described implementations. Further, operations described herein may occur sequentially or certain operations may be processed in parallel, or operations described as performed by a single process may be performed by distributed processes.

The illustrated logic of FIGS. 6-9 may be implemented in software, hardware, programmable and non-programmable gate array logic or in some combination of hardware, software, or gate array logic.

FIG. 10 illustrates an architecture 1000 of a computer system that may be used in accordance with certain implementations of the invention. Client computers, server computers, storage controllers and/or the admin client computer may implement computer architecture 1000. The computer architecture 1000 may implement a processor 1002 (e.g., a microprocessor), a memory 1004 (e.g., a volatile memory device), and storage 1010 (e.g., a non-volatile storage area, such as magnetic disk drives, optical disk drives, a tape drive, etc.). An operating system 1005 may execute in memory 1004. The storage 1010 may comprise an internal storage device or an attached or network accessible storage. Computer programs 1006 in storage 1010 may be loaded into the memory 1004 and executed by the processor 1002 in a manner known in the art. The architecture further includes a network card 1008 to enable communication with a network. An input device 1012 is used to provide user input to the processor 1002, and may include a keyboard, mouse, pen-stylus, microphone, touch sensitive display screen, or any other activation or input mechanism known in the art. An output device 1014 is capable of rendering information from the processor 1002, or other component, such as a display monitor, printer, storage, etc. The computer architecture 1000 of the computer systems may include fewer components than illustrated, additional components not illustrated herein, or some combination of the components illustrated and additional components.

The computer architecture 1000 may comprise any computing device known in the art, such as a mainframe, server, personal computer, workstation, laptop, handheld computer, telephony device, network appliance, virtualization device, storage controller, etc. Any processor 1002 and operating system 1005 known in the art may be used.

The foregoing description of implementations of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the implementations of the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the implementations of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the implementations of the invention. Since many implementations of the invention can be made without departing from the spirit and scope of the implementations of the invention, the implementations of the invention reside in the claims hereinafter appended or any subsequently-filed claims, and their equivalents. 

1. An article of manufacture comprising a computer readable storage medium including code for locating data, wherein the code when executed by a processor of a computer causes operations to be performed, the operations comprising: storing mapping information in a metadata store, wherein for each file, the mapping information includes source blocks that indicate locations of source blocks for the file, one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks, and a session identifier that identifies a session, wherein the session is a set of copy service relationships that represent a set of data being maintained in a consistent state; providing mapping information for a file to each of multiple client computers coupled to the metadata store; determining that a copy service has copied source blocks to target blocks for the file, wherein the target blocks are a copy of the source blocks for the file; updating the mapping information in the metadata store with locations of the target blocks; and for each of the multiple client computers, determining whether the mapping information for the file should be updated at that client computer to refer to the target blocks based on whether the target blocks are accessed as often as blocks for the file that the client computer is currently accessing; and providing updated mapping information to that client computer in response to determining that the mapping information should be updated to refer to the target blocks based on determining that the blocks for the file that the client computer is currently accessing are being accessed more often than the target blocks.
 2. The article of manufacture of claim 1, wherein the operations further comprise: receiving a request for locations of blocks for the file when the file is opened; determining which blocks associated with the file should be made available in response to the request; and sending the mapping information for the determined blocks.
 3. The article of manufacture of claim 2, wherein the operations further comprise: determining which of the blocks should be made available based on availability of the blocks.
 4. The article of manufacture of claim 1, wherein the mapping information is sent to a client computer in response to a request for the mapping information and wherein the client computer uses the mapping information to access the file.
 5. The article of manufacture of claim 1, wherein the updated mapping information is automatically sent to a client computer and wherein the client computer uses the updated mapping information to access the file.
 6. An article of manufacture comprising a computer readable storage medium including code for accessing a copy of data when a source of the data is inaccessible, wherein the code when executed by a processor of a computer causes operations to be performed, the operations comprising: determining that a storage controller has failed; determining that source blocks for files on the failed storage controller are unavailable; determining whether it is appropriate to switch indicators pointing to the source blocks to point to target blocks using one or more first policies or to allow error processing to occur; for each of the files on the failed storage controller, in response to determining that it is appropriate to switch indicators, locating multiple target blocks that are copies of the unavailable source blocks for that file using data in a metadata store, wherein the metadata store stores, for each of the files, mapping information that includes source blocks that indicate locations of source blocks for the file and one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks; selecting target blocks for that file from among the multiple target blocks using one or more second policies; switching indicators pointing to the source blocks to point to the selected target blocks in the metadata store, wherein the selected target blocks for that file become new source blocks; determining which of the client computers should be sent updated mapping information from the metadata store for the selected target blocks for that file based on which of the client computers had been accessing the source blocks that became inaccessible; and updating mapping information at each of the determined client computers to access the selected target blocks for that file instead of the source blocks.
 7. The article of manufacture of claim 6, wherein the selected target blocks had been in a continuous copy relationship with the source blocks that was suspended when the source blocks became unavailable.
 8. The article of manufacture of claim 6, wherein the operations further comprise: creating a copy of the selected target blocks.
 9. The article of manufacture of claim 6, wherein the source blocks are unavailable on a virtual device being managed by a SAN aware file system and wherein the operations further comprise: determining that an I/O operation accessing the source blocks has failed; and retrying the I/O operation by accessing the selected target blocks in response to updating the mapping information.
 10. The article of manufacture of claim 6, wherein the source blocks are unavailable due to the storage controller failure.
 11. A system for locating data, comprising: circuitry causing operations to be performed, the operations comprising: storing mapping information in a metadata store, wherein for each file, the mapping information includes a filename, source blocks that indicate locations of source blocks for the file, one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks, and a session identifier that identifies a session, wherein the session is a set of copy service relationships that represent a set of data being maintained in a consistent state; providing mapping information for a file to each of multiple client computers coupled to the metadata store; determining that a copy service has copied source blocks to target blocks for the file, wherein the target blocks are a copy of the source blocks for the file; updating the mapping information in the metadata store with locations of the target blocks; and for each of the multiple client computers, determining whether the mapping information for the file should be updated at that client computer to refer to the target blocks based on whether the target blocks are accessed as often as blocks for the file that the client computer is currently accessing; and providing updated mapping information to that client computer in response to determining that the mapping information should be updated to refer to the target blocks based on determining that the blocks for the file that the client computer is currently accessing are being accessed more often than the target blocks.
 12. The system of claim 11, wherein the operations further comprise: receiving a request for locations of blocks for the file when the file is opened; determining which blocks associated with the file should be made available in response to the request; and sending the mapping information for the determined blocks.
 13. The system of claim 12, wherein the operations further comprise: determining which of the blocks should be made available based on availability of the blocks.
 14. The system of claim 11, wherein the mapping information is sent to a client computer in response to a request for the mapping information and wherein the client computer uses the mapping information to access the file.
 15. The system of claim 11, wherein the updated mapping information is automatically sent to a client computer and wherein the client computer uses the updated mapping information to access the file.
 16. A system for accessing a copy of data when a source of the data is inaccessible, comprising: circuitry causing operations to be performed, the operations comprising: determining that a storage controller has failed; determining that source blocks for files on the failed storage controller are unavailable; determining whether it is appropriate to switch indicators pointing to the source blocks to point to target blocks using one or more first policies or to allow error processing to occur; for each of the files on the failed storage controller, in response to determining that it is appropriate to switch indicators, locating multiple target blocks that are copies of the unavailable source blocks for that file using data in a metadata store, wherein the metadata store stores, for each of the files, mapping information that includes source blocks that indicate locations of source blocks for the file and one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks; selecting target blocks for that file from among the multiple target blocks using one or more second policies; switching indicators pointing to the source blocks to point to the selected target blocks in the metadata store, wherein the selected target blocks for that file become new source blocks; determining which of the client computers should be sent updated mapping information from the metadata store for the selected target blocks for that file based on which of the client computers had been accessing the source blocks that became inaccessible; and updating mapping information at each of the determined client computers to access the selected target blocks for that file instead of the source blocks.
 17. The system of claim 16, wherein the source blocks are unavailable due to the storage controller failure.
 18. The system of claim 16, wherein the selected target blocks had been in a continuous copy relationship with the source blocks that was suspended when the source blocks became unavailable.
 19. The system of claim 16, wherein the operations further comprise: creating a copy of the selected target blocks.
 20. The system of claim 16, wherein the source blocks are unavailable on a virtual device being managed by a SAN aware file system and wherein the operations further comprise: determining that an I/O operation accessing the source blocks has failed; and retrying the I/O operation by accessing the selected target blocks in response to updating the mapping information.
 21. A system for locating data, comprising: means for storing mapping information in a metadata store, wherein for each file, the mapping information includes a filename, source blocks that indicate locations of source blocks for the file, one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks, and a session identifier that identifies a session, wherein the session is a set of copy service relationships that represent a set of data being maintained in a consistent state; means for providing mapping information for a file to each of multiple client computers coupled to the metadata store; means for determining that a copy service has copied source blocks to target blocks for the file, wherein the target blocks are a copy of the source blocks for the file; means for updating the mapping information in the metadata store with locations of the target blocks; and for each of the multiple client computers, means for determining whether the mapping information for the file should be updated at that client computer to refer to the target blocks based on whether the target blocks are accessed as often as blocks for the file that the client computer is currently accessing; and means for providing updated mapping information to that client computer in response to determining that the mapping information should be updated to refer to the target blocks based on determining that the blocks for the file that the client computer is currently accessing are being accessed more often than the target blocks.
 22. A system for accessing a copy of data when a source of the data is inaccessible, comprising: means for determining that a storage controller has failed; means for determining that source blocks for files on the failed storage controller are unavailable; means for determining whether it is appropriate to switch indicators pointing to the source blocks to point to target blocks using one or more first policies or to allow error processing to occur; for each of the files on the failed storage controller, in response to determining that it is appropriate to switch indicators, means for locating multiple target blocks that are copies of the unavailable source blocks for that file using data in a metadata store, wherein the metadata store stores, for each of the files, mapping information that includes source blocks that indicate locations of source blocks for the file and one or more target blocks that represent one or more copies of the source blocks and provide locations of copies of the source blocks; means for selecting target blocks for that file from among the multiple target blocks using one or more second policies; means for switching indicators pointing to the source blocks to point to the selected target blocks in the metadata store, wherein the selected target blocks for that file become new source blocks; means for determining which of the client computers should be sent updated mapping information from the metadata store for the selected target blocks for that file based on which of the client computers had been accessing the source blocks that became inaccessible; and means for updating mapping information at each of the determined client computers to access the selected target blocks for that file instead of the source blocks. 